Allogeneic Blood and Marrow Transplantation (BMT) is a curative therapy performed on over 15,000 individuals per year, according to the IBMTR, at a cost of approximately $3.5 billion dollars annually. Currently, G-CSF primed peripheral blood is the most commonly used donor source for adult recipients of an allogeneic BMT. The Canadian Blood and Marrow Transplantation Group Clinical Trials Network (CBMTG-CTN), which includes all 23 BMT centers in Canada, was established 11 years ago. Until the establishment of the NHLBI/NCI funded BMT CTN in 2001, the CBMTG-CTN, which includes all BMT patients in Canada, was the largest clinical trials group in North America. The CBMTG-CTN performed a definitive randomized trial in 228 patients and established that related G-CSF stimulated peripheral blood (G-PB) is superior in outcome to unstimulated bone marrow in adult BMT recipients (Couban et al., Blood, 2002). Recently, a small study demonstrated that, as a donor source, G-CSF stimulated BM (G-BM) has a significantly lower rate of graft-versus-host disease than does G-PB and affects long term outcome. A large randomized study is required to definitively establish whether G-BM will give a superior recipient outcome compared to G-PB. Currently, the CBMTG-CTN is the only group capable of performing such a trial, and it has the additional advantages of having performed preliminary trials evaluating G-BM as a donor source. The CBMTG-CTN will also utilize excellent NIH and CIHR funded laboratories to correlate immunological outcomes with this study. The health care system in Canada presents unique opportunities to perform comprehensive quality of life evaluations and economic impact studies in conjunction with this trial. This application represents what will be a pivotal study to establish whether G-BM represents the best donor option for BMT. The immunological studies will be used to develop innovative strategies to improve patient outcomes with graft engineering of G-PB. This study will have a worldwide impact on how BMT is performed in the future.